Various silver halide color photographic materials and various color image forming methods using them are widely used at present.
The requirements with respect to the silver halide color photographic materials have increased markedly in recent years. For example, the rapid processing performance of color photographic paper must be improved and at the same time, the photographic paper must be fed in a stable manner while keeping the printing conditions constant to finish a large quantity of prints in a short time.
In order to feed such a paper in a stable manner while keeping the printing conditions constant, variation in the sensitivity and gradation of the color photographic paper from lot to lot must not occur and a change in sensitivity and gradation must not occur even when the color photographic paper is stored over a long period of time.
Variation in sensitivity and gradation from lot to lot and change in sensitivity and gradation during long-term storage are particularly marked for the red-sensitive emulsion layers. A solution to these problems is definitely required.
The above lot-to-lot variation frequently occurs because the red-sensitive sensitizing dyes in the red-sensitive emulsion layers desorped from silver halide grains in the coating solutions with the passage of time, and, as a result, desensitization occurs. Various methods have been proposed to solve this problem with respect to the desensitization of the coating solutions with the passage of time. For example, the long-term stability of the coating solutions can be greatly improved by using stilbene compounds as described in JP-A-59-135461 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). JP-A-60-225147 discloses a method wherein a tetradecahedral silver chlorobromide grain emulsion sensitized with a certain red-sensitive sensitizing dye is used to improve the long-term stability of the coating solutions. However, these methods are insufficient to prevent a change in the sensitivity and gradation of photographic materials from occurring during long-term storage, though the long-term stability of the coating solutions is improved and variation of color photographic paper from lot to lot is reduced.
With regard to an improvement in rapid processing performance, the processing stages have been simplified and high-temperature development is generally conducted. In order to shortening the development time with high-temperature development, it is very important to improve the development rate in color development. It is known that this is greatly affected by the shape, size and composition of the silver halide grains and the condition of the color developing solutions. An improvement in rapid processing performance has been recently achieved by improving the silver halide emulsion grains and the compositions and conditions of the color developing solutions on the basis of this knowledge.
However, the conveying speed in automatic processors is increased in rapid processing. Thus, the frequency of sensitization and desensitization caused by scratching and pressure in various locations inside and outside an automatic processor is increased. Thus, it is necessary for the photographic materials to have high resistance to pressure.
Many studies have been reported that fogging or desensitization is caused by silver halide grains as an element of a photographic material when physical pressure is applied thereto.
For example, the deformation of silver halide grains caused by pressure, the strain of the crystals, the defects of the crystal latice in the deformed state and the influence of the deformation on the distribution of latent image centers are fully described in J. Photo. Sci., 21, 221 to 226 (1973).
Methods for preventing fogging or desensitization from being caused by pressure include methods wherein pressure is not allowed to reach silver halide, or various gelatin polymers and various organic compounds are used in the protective layer, intermediate layer and silver halide-containing layers of the photographic materials. For example, a method using alkyl phthalates described in U.K. Patent 738,637, a method using alkyl esters described in U.K. Patent 738,639, a method using hydrophilic compounds, particularly polyhydric alcohols described in U.S. Pat. No. 2,960,404, a method using high-boiling organic compounds immiscible with hydrophilic binders described in JP-A-53-85421 and a method using alkyl acrylates and organosilver salts described in JP-B-53-28086 (the term "JP-B" as used herein means an "examined Japanese patent publication") are known.
However, these methods have little effect on high pressure. Moreover, these methods have disadvantages in that the surfaces of the photographic materials become excessively sticky and the photographic characteristics of the photographic materials are adversely affected. Thus, the primary object cannot be achieved.